The present invention relates generally to an exhaust system for automotive vehicles. More particularly, the present invention relates to simulating real world conditions to create exhaust system components for testing on-board diagnostics system.
Emissions controls systems are generally used as a means for limiting pollutants from the exhaust gas of an internal combustion engine. These emissions control systems limit, among other things, carbon monoxide (CO), hydrocarbon (HC), and nitrous oxide (NOx) from engine exhaust gases in a variety of methods.
As it is known in the industry, the performance of a catalytic converter, and specifically catalytic converter bricks contained therein, varies as a function of time due to conditions such as chemical and thermal breakdown. The variance in performance of a catalytic converter brick is detected in the portion of a vehicle""s on-board diagnostics (OBD) systems that detects emissions and emissions variances. To evaluate and verify the performance of OBD systems, experimental exhaust systems are created to verify in a laboratory setting that an OBD system is functioning properly. To do this, aged production catalytic bricks are needed to simulate the testing conditions necessary for verifying that an OBD is working properly.
It is known in the industry that levels of tailpipe emissions (HC, CO, and NOx) are typically higher in vehicles with catalytic converter bricks placed in vehicles without a mileage accumulation than with a few hundred-mile accumulation. It is thus standard practice to stabilize (normalize) these catalytic converter bricks which are to be used to evaluate an OBD system. One method to accomplish this normalization process is to pass exhaust gases through the catalytic converter brick using an engine dynamometer stand, in effect simulating a mileage accumulation period. Unfortunately, this dynamometer period is both costly and time consuming.
The normalization step is part of a typical four-stage process for creating catalytic converter bricks with specific performance characteristics that are used to evaluate OBD systems under real world conditions. The four-stage process for creating the catalytic converter brick under the current methodology includes first determining the type of catalytic converter brick that will be placed in the exhaust system based upon the characteristics of the particular exhaust system. Next, the catalytic converter brick is thermally aged to a predetermined condition. Then, the catalytic converter brick is chemically aged to a predetermined condition. Finally, the catalytic converter brick is normalized to a predetermined condition. Each step is described in more detail below.
First, the type, density and size of a catalytic converter brick in an exhaust system is determined based upon the individual characteristics of the exhaust system that it will be placed in. Second, the catalytic converter brick is thermally aged for a predetermined time at a predetermined temperature to simulate real world thermal breakdown of the catalytic converter brick at a particular location in an exhaust system. Third, the catalytic converter brick is chemically aged for a predetermined time at a predetermined concentration of chemical contaminate to simulate real world chemical breakdown of the catalytic converter brick at a particular location in an exhaust system. Finally, the catalytic converter brick is normalized by placing the catalytic converter brick in an exhaust system that is placed on an engine dynamometer stand for a predetermined amount of hours to simulate real world chemical and thermal breakdown as a result of typical mileage accumulation of a catalytic converter brick on a vehicle. This normalized catalytic converter brick will have a particular emissions characteristic (within a certain parameter) that has been previously verified when it is placed in a laboratory exhaust system. If the OBD systems is functioning properly when placed on the laboratory exhaust system, it will read a similar emissions characteristic for the normalized catalytic converter brick.
It would therefore be desirable to provide a normalized catalytic converter brick, hereinafter an emissions threshold catalytic brick, without the accompanying mileage accumulation in order to evaluate and verify the operation of OBD systems under real world conditions.
It is an object of the present invention to provide an emissions threshold catalytic brick without an accompanying mileage accumulation that may be used for testing of an OBD exhaust systems in real world situations.
The above object is achieved by providing a method of normalizing an emissions threshold catalytic brick without the need for mileage accumulation by placing the emissions threshold catalytic brick immediately after thermal and chemical aging in an exhaust gas circulating oven.
The above object is also part of an overall OBD Emissions Threshold Catalyst Process for evaluating an OBD system in a laboratory environment. The process comprises the steps of determining the location, type, size and density of an emissions threshold catalytic brick based upon the characteristics of the exhaust system in which the emissions threshold catalytic brick will be used; determining an aging time and temperature for thermal aging of the particular emissions threshold catalytic brick based upon these same characteristics; determining a chemical aging process of the particular emissions threshold catalytic brick based upon these same characteristics; normalizing the emissions threshold catalytic brick by placing it in an exhaust gas circulating oven at a particular temperature, time, and air/fuel stoichiometry based upon these same characteristics, and placing the emissions threshold catalytic brick in an experimental exhaust system with these same characteristics to verify that an OBD exhaust system is functioning properly.
Other objects and advantages of the present invention will become apparent upon considering the following detailed description and appended claims, and upon reference to the accompanying drawings.